Apparatus for the continuous self-regulating gravity-flow mixing of pourable granular material

ABSTRACT

A combination of apparatus for the continuous, self-regulating, gravity-flow mixing of different component streams of a pourable or flowing granular material wherein a plurality of individual discharge conduits from different supply vessels and/or supply zones open into a grid of feed compartments at the upper end of a vertical receiving container of rectangular cross section having a unidimensionally narrowing discharge zone terminating in a discharge slot at the lower end of the container and an unobstructed stabilizing zone interconnecting the discharge zone with the feed compartments, with means to adjust the flow of granular material through the discharge slot.

United States Patent [72] Inventor Friedrich Jaeger Bad Hersfeld, Germany [2 I 1 Appl. No. 822,184 [22] Filed May 6, I969 [45] Patented Mar. 30, 1971 [73] Assignee Glanzstoff A G Wuppertal, Germany [32] Priority May 10, 1968 [3 3] Germany [3l] P- 17 56 344.9

[54] APPARATUS FOR THE CONTINUOUS SELF- REGULATING GRAVITY-FLOW MIXING F POURABLE GRANULAR MATERIAL 8 Claims, 3 Drawing Figs. [52] U.S. Cl 259/180, 259/4, 259/150 [51] Int. Cl B0lf /00 Field of Search 259/4, 180, 150, 18, 36

[56] References Cited UNITED STATES PATENTS 829,127 8/1906 Strauss 259/ 2,486,200 10/1949 OConnor 259/ 3,155,377 11/1964 Godman 259/180 3,158,362 11/1964 Seifarth 259/180 Primary ExaminerMarvin A. Champion Assistant Examiner-Robert A. Hafer A tt0rney-JOhnSt0I1, Root, Okeeffe, Keil, Thompson and Shurtleff ABSTRACT: A combination of apparatus for the continuous, self-regulating, gravity-flow mixing of different component streams of a pourable or flowing granular material wherein a plurality of individual discharge conduits from different supply vessels and/or supply zones open into a grid of feed compartments at the upper end of a vertical receiving container of rectangular cross section having a unidimensionally narrowing discharge zone terminating in a discharge slot at the lower end of the container and an unobstructed stabilizing zone interconnecting the discharge zone with the feed compartments, with means to adjust the flow of granular material through the discharge slot.

APPARATUS FOR THE CONTINUOUS SELF- REGULATTNG GRAVITY-FLOW MIXING OF POURABLE GRANULAR MATERIAL This invention generally relates to apparatus for the continuous withdrawal and gravity-flow mixing of a pourable, granular material as it is discharged in fractional or component amounts from different supply or storage vessels and/or different supply zones of one or more vessels. Such apparatus may also be referred to as a gravity-flow solids blender and provides a means of improving the homogeneity of a granular mixture.

The term pourable granular material" is applied to particles or granules of a wide variety of substances which exhibit a substantially uniform particle or grain size and are normally resistant toward adhesion, i.e. there are no adhesive forces sufficient to cause an uncontrollable agglomeration or thermal growth of particle size. For purposes of the present disclosure, the expression pourable granular material" includes all particles or granulates as described in the periodical chemic-lngenieur-Technik," Vol. 30, 1958, No. 3, pages l44-l46. The apparatus of the invention is particularly suitable for the gravity-flow mixing of thermoplastic polymer granulates,'e.g. as a feed into injection molding machines, extruders, meltspinning devices and the like for the production of molded articles, films, filaments and similar products. The apparatus is also adapted to handle particulated or pelletized foodstuffs or fertilizers as well as seed grains and the like. 7

in the blending or mixing of a pourable granular material, it is not only desirable to achieve a thorough homogenization of the mixture but it is also important to carefully proportion the fractional amounts of the component materials being mixed, in a discontinuous mixing procedure, the distribution by weight or by volume of the fractional amounts for achieving a complete mixing generally presents no problem. This is not true when the mixing procedure is carried out continuously, especially when it is desirable to employ a gravity-flow blending or mixing to avoid excessive apparatus and expense in the movement of the particles and/or to avoid abrasion and attrition or comminution of the granular material. In this case, it has been extremely difficult to solve the problem of maintaining a constant and uniform control over the amount of granular material flowing in a large number of individual streams. For the most part, automatic control means for existing apparatus are quite complicated and expensive, and self-regulating gravity-flow devices still require considerable development.

One object of the present invention is to provide apparatus for the gravity-flow withdrawal and recombination of a large number of component streams of pourable granular material such that this mixing procedure can be accomplished without the use of complicated and expensive measuring and regulating devices which are highly susceptible to disturbances or malfunctioning in their operation.

Another object of the invention is to provide a gravity-flow mixing apparatus which is easily constructed and maintained with an absolute minimum of moving parts.

Yet another object of the invention is to provide a gravityflow mixing apparatus which is adapted to handle a wide variety of pourable granular materials under continuous, selfregulating feed supply from different supply vessels and/or supply zones.

These and other objects and advantages of the invention will become more apparent upon consideration of the following detailed disclosure.

it has now been found, in accordance with the invention, that a uniform and self-regulating continuous flow of the pourable granular material can be achieved in a gravity-flow mixing apparatus which comprises in combination: at least one supply vessel associated with a plurality of discharge conduits for gravity-flow withdrawal of the granular material from different supply zones thereof; an elongated vertical receiving container of rectangular cross section arranged below said supply vessel, said container having a unidimensionally narrowing discharge zone at its lower end formed by oppositely disposed walls slanting downwardly and inwardly with a narrow discharge slot at their bottom end, the angle of aperture formed by said slanting walls being smaller than 0.8 times the difference between and twice the angle of slide of the granular material, and said container having a feed grate arranged at its upper end composed of a plurality of individual compartments subdividing the rectangular cross section of the container into a grid of feed zones in feed connection with said discharge conduits, that portion of the rectangular container between its discharge zone and said feed zones being essentially free of any obstruction to fonn a stabilizing zone which has a vertical height greater than the product of its width and the tangent of the angle of slide of said granular material; and means to regulate the rate of flow of said granular material through said discharge slot.

The term angle of aperture" is employed herein to define the angle between the two slanting or converging walls of the discharge zone which present an unidimensionally narrowing rectangular cross section terminating in an elongated discharge slot or narrow rectangular aperture at the bottom of an otherwise uniformly rectangular receiving vessel. This discharge slot is preferably combined with means to regulate the discharge of granular material therethrough, e.g. a movable gate or door which permits the effective width of the discharge slot to be varied, preferable together with means to convey the granular material away from the discharge slot such as a rotating drum, a conveyor belt or any similar moving surface.

For purposes of definition herein, the widt or breadth" of various rectangular cross sections of the receiving container are measured in the direction in which the discharge zone is narrowed by its slanting walls. The "length" or depth of the rectangular vessel remains constant and is thus measured in the longitudinal direction of the discharge slot, while the height" of the receiving container and its stabilizing and discharge zones are measured inthe'vertical direction.

The term angle of slide" has reference to the granular material being mixed and is sometimes referred to as the angle of slope" or pour angle" which is formed by pouring a conically-shaped mass of particles in which the individual particles freely slide or fall down the outer surface of the cone, the angle being measured between this conical surface and the horizontal. The angle of slide may also be defined as the angle of minimum slope, measured from the horizontal, at which any pourablegranular material or similar loose solid will flow. By way of example, a polyethylene terephthalate granulate with a uniform particle size of 2X3X4 mm has an angle of slide of approximately 40. This angle of slide can be readily determined for any other granular material.

The entire receiving container of the invention is adapted to provide a discharge bed or plurality of superimposed discharge layers in which the granular material is moved downwardly solely by the force of gravity, i.e. so as to pass slowly through the container from top to bottom as controlled by the constricted discharge zone and removal of material through the narrow discharge slot. ln a stabilization of this discharge bed, it will be understood that the velocity of the individu'al granular particles in all lines of stream over a given cross section is nearly constant. in the ideal case, such a stabilized stream presents a so-called coherent or graft" stream.

In order to achieve the desired stabilizing zone in the receiving container, Le. a stabilized discharge bed, it is essential to employ a rectangular container with particular dimensions as noted above which are dependent upon the angle of slide of the granular material. The depth of the receiving container remains constant over both the stabilizing and discharge zones thereof. The breadth or width also remains constant in the stabilizing zone while becoming narrower in the discharge zone to provide the unidimensionally narrowing rectangular cross section. In addition, the discharge slot must be sufficiently narrow to have a damming or delaying effect on the rate of flow of granular material through the receiving container. in

general, the width of the discharge slot should be smaller than approximately 0.1 of the width of the rectangular receiving container, i.e. the width of the stabilizing zone corresponding to the maximum width of the discharge zone. When this particular construction of the receiving container is combined with the require feed grate at the upper end of the container, it is possible to achieve the desired self-regulating withdrawal of partial streams or different components of the granular material as more fully described hereinafter.

A preferred embodiment of the combination of apparatus according to the invention is shown in detail by the drawing in which:

FIG. I is a partly schematic side elevational view of the receiving container with its associated discharge conduits feeding into the top end and suitable discharge means at the bottom end, selected portions being cut away at the top and bottom;

FIG. 2 is a partly schematic top plan view of the receiving container of FIG. 1;

FIG. 3 is a partly schematic side elevational view of the receiving container (shown in cross section) in combination with the required discharge elements and illustrating the use of two different supply vessels in which partial amounts of a granular material are drawn off from different supply zones and then reunited with each other in the receiving container.

Referring first to FIGS. 1 and 2, the apparatus of the invention essentially includes the elongated and vertically positioned receiving container 1 with an upper feed or dosing zone 2, an intermediate stabilizing zone 3 and a lower or bottom discharge zone 4 with two oppositely disposed walls 8 slanting or converging inwardly at the required angle of aperture down to the discharge slot 5. A feed grate or grid insert 6 is contained within the four vertically positioned walls I of the receiving container so as to form the feed zone 2 with a total of 30 individual grid or feed compartments 11, all of which have the same quadratic cross section and extend vertically downwardly from the open top of the container 1.

The lower ends of a corresponding 30 discharge conduits 9 are inserted vertically downwardly into the top of the receiving container 1 so as to open into the individual feed zones formed by each grid compartment ll, preferably so as to terminate at about the same vertical level on a plane intermediate the top and bottom of each of the compartments and located centrally or symmetrically within the quadratic crosssectional area of each compartment. These discharge or individual feed conduits 9 can come from two supply bins or vessels (shown only in FIG. 3), one of which contains a granular component A and the other of which contains a different granular component B. By arranging the discharge conduits 9 as illustrated in FIG. 2 so that adjacent feed zones 11 of the feed grate 6 receive a different component A or B in each case, the effect is obtained not only of providing a self-regulating proportioning of both components, e.g. in a ratio of 1:1 as illustrated here, but also of simultaneously providing a good basis for achieving a more homogeneous mixture. Of course, the relative position of each discharge or feed conduit 9 is not important in terms of a self-regulating and equalized dosage of the partial amounts of each components. Therefore, when further homogenization is not a serious problem, it is sufficient to permit the 15 discharge conduits from each supply vessel to open into an 15 randomly positioned grid or feed compartments.

As can be seen from FIG. 1, the bottom ends of the discharge tubes or conduits 9 lie at about the same height. However, it is a further advantage of the apparatus of the invention that an exact placement of these bottom ends of the conduits 9 is not a critical feature. Good results are achieved even if the discharge conduits 9 terminate at random heights or vertical levels within the grid compartments 1], and this greatly simplifies the installation of the tubular conduits. Thus, it is preferable to employ tubular discharge conduits having a circular cross section, and although they are most suitably arranged in fixed positions laterally or horizontally of one another to fall within their respective grid compartments, they can be adjustably or randomly fastened in their vertical position so that they need not have an extremely accurately measured length or be fastened so as to place undesirable strains or stresses on the container or the conduits themselves.

If it is desirable to deliver the two components A and B in a different feed ratio, e.g. 2:1, with the apparatus as illustrated in FIGS. 1 and 2, then one can simply choose the corresponding proportion of the number of discharge conduits from each of the two supply vessels, i.e, so that there is a ratio of conduits with component A to conduits with component B of 20: I0.

Naturally, it is also possible with the apparatus of the invention to withdraw and proportion more than two components in the described manner and in required amounts from more then two or a large number of different supply vessels under similar conditions of self-regulating flow.

The arrangement of two or even more supply bins or vessels 10 above the receiving container 1 and in feed connection therewith through a plurality of discharge conduits 9 is illustrated in FIG. 3. Thus, the pourable granular material is not only withdrawn from different supply vessels 10 but also from different supply zones within each vessel where the discharge conduits open into the vessel at random heights and preferably at random cross-sectional positions in a manner which is conventional for obtaining random samples from a single supply vessel. Thus, the top ends of the conduits 9 preferably project inwardly and upwardly into the interior of the vessels 10 so as to terminate at different levels or in different supply zones. This combination of withdrawing pourable granular material from different supply zones as well as different supply vessels is especially advantageous if the components A and B in each of the supply vessels 10 are themselves already mixtures of two or more components. When operating continuously, it is desirable to keep the vessels I0 filled by any suitable feed of the granular material at the top end of these vessels; and if desired, a series of supply vessels can lead into the two illustrated in FIG. 3 so as to enhance the conventional cross-mixing of partial streams of the granular material.

In order to avoid repetitive details of the feed supply through conduits 9, only a few of these conduits at one vertical cross section of the receiving container 1 are shown in their entirety in FIG. 3 as they extend from the supply vessels I0 downwardly into the compartments ll of the feed grate 6. It will be understood that all of these conduits 9 provide a complete feed connection as schematically illustrated in FIG. 2 with reference to the components A and B.

The form of the feed grate or grid insert 6 with its quadratic compartments 11 extending vertically downwardly from the top of container 1 represents an especially preferred embodiment. These grid compartments 11 can naturally assume other cross-sectional shapes, e.g. rectangular, circular, elliptical, hexagonal, etc., and may also be of different sizes. However, it is important the ratio of the cross-sectional area of those compartments II being supplied with component A to the total area of all of the compartments be the same as the ratio of the volume of component A to the volume of the entire mixture. In other words, it is desirable to maintain the throughput by volume of any given component constant over the entire apparatus.

It is also feasible to provide additional baffied inserts (not shown) within the feed zone 2 in order to further subdivide the individual streams entering into the container 1 from the conduits 9. For example, a second feed grate or grid insert can be arranged below that shown such that its vertical walls intersect and separate the streams flowing downwardly from the first feed grate. It is extremely important, however, to avoid any such baffles, stream guiding inserts or similar obstruction in the stabilizing zone 3 which must have a predetermined vertical height within the container 1 above the discharge zone 4.

The working principle of the apparatus of the invention can be readily explained in connection with the drawing. The pourable granular material arrives from the supply vessel or vessels 10, i.e. from the different supply zones, in the direction of the arrows A and B as shown in FIG. 1 to represent two different components. The granular material initially falls into the empty receiving container 1 where the discharge slot 5 is closed off by a suitable gate or sliding door 12 in cooperation with the rotatable discharge drum 7. The container 1 is thus completely filled up to the level of the bottom ends of the discharge conduits 9 and these remain filled up into the supply vessels It). At the beginning of continuous operation, the entire apparatus is then filled completely with granular material while further flow from the discharge conduits 9 is blocked off where the granular material itself closes off their bottom ends.

The gate 12 is then opened to such an extent that the total efiective area of the discharge slot opening 5 is less than or at the most equal to the free or open cross section of all of the discharge conduits 9. The granular material then flows or streams through the container 1 so as to temporarily unblock the bottom ends of the discharge conduits 9, thereby permitting a continuous but controlled flow of the various partial streams from the supply vessels 10. There may be an intermittent blocking and unblocking of the discharge conduits 9 during operation of the apparatus as the granular material is withdrawn by gravity-flow therethrough. The self-regulating feed is essentially imposed at the moment at which the bottom ends of these tubes or conduits 9 are unblocked. Fresh granular material is continuously supplied to the vessels It) to maintain a level which is consistently above the uppermost feed intake or feed zone of the supply vessels where granular material is being withdrawn through conduits 9.

By rotating the conveyor or discharge drum 7 in the direction of its arrow, there is achieved a steady and uniform removal of the granular material through the discharge slot 5 together with a somewhat further mixing of the individual particles. This discharge drum represents the only moving element of the apparatus aside from the gate 12, and this drum can be modified or even removed if the granular material is discharged directly into another container or other transporting means. The gate 12 is usually opened to provide a predetermined or easily adjustable discharge gap and requires little or not adjustment during operation. Thus, the entire apparatus operates essentially only by gravity-flow with a selfregulating proportioning of the partial streams of each component.

The stabilizing zone 3 of the receiving container 1 is essential and requires a certain minimum vertical height above the discharge zone 4 in order to ensure a uniform vertical rate of flow of the granules or particles across a horizontal cross section at the upper end of the containerl and especially within the individual feed zones 2. Thus, the bed or horizontal layers of particles in the container 1 must be sufficiently stabilized so that their downward movement uniformly unblocks the lower rims of the discharge conduits 9. Each portion or partial stream of the granular material then slides or flows in equal proportions in the individual compartments ll of the feed grate 6. With compartments 1] and conduits 9 of uniform size and shape, the granular material from each supply vessel 10 flows into the container 1 in likewise equally proportioned amounts due to the uniform unblocking of the lower ends of the discharge conduits 9. In the absence of the stabilizing zone 3 or with an insufficient height of this zone, the self-regulating flow of the granular material with equalized proportions of the individual streams from one or more supply vessels and/or supply zones cannot be achieved.

in general, the stabilization of the discharge bed or layers in container 1 occurs to the desired extend provided that the width of the stabilizing zone 3 is less than 1500 mm. and preferably less than 800 mm., i.e the width measured in the same direction as the width of the discharge slot 5 or the direction in which the discharge zone 4 converges inwardly down to the discharge slot. With stabilizing zone widths of more than l500 mm., the stream or flow of granular material tends to become unstable, i.e. every high stabilizing zone is not longer successful in achieving an essentially coherent stream or constant rate of vertical flow of the bed below the feed zone and hence within the individual grid or feed compartments.

Likewise, it is essential for the angle of aperture of the slanting walls of the discharge zone and the height of the stabilizing zone to have the prescribed dimensions dependent upon the angle of slide of the granular material being mixed. preferably with all components of this granular material having the same or uniform particle size. Also, the uniform square or rectangular cross section over the entire height of the container 1, especially in the stabilizing zone 3, is an essential feature of the apparatus. Finally, it is necessary to provide a plurality of feed compartments at the upper end of the receiving container, i.e. as formed by the feed grate having a series of intersecting or interconnected vertical planar walls subdividing the cross-sectional area into carefully proportioned feed zones.

The upper end of the receiving container 3 and its vertical feed compartments ll can remain open or a suitable cover with openings for the conduits 9 can be incorporated to avoid contamination from the surrounding atmosphere or to provide a dusttight closure where this is deemed necessary.

The feed grate 6 should have a vertical height to receive the bottom ends of the conduits 9 at a distance above the lower end or edge of the grate sufficient to ensure an at least partial filling of the feed compartments during continuous operation. This distance is determined in part by the relative cross-sectional areas of the conduits 9 and compartments ll, respectively, and in part by the angle of slide of the granular material itself. The rate of withdrawal of the granular material may also affect this placement of the conduit discharge openings, but this withdrawal rate is usually sufficiently-slow as to avoid a complete emptying of a feed compartment. Otherwise, the maximum height of the feed zone is limited by practical considerations of maintaining the overall height of the receiving container as small as possible within a given space.

Because the granular materials are drawn off at approximately equal vertical velocity through the stabilization of flow conditions in the stabilizing zone of the discharge bed, the apparatus of the invention provides means of setting up definite proportions between the cross-sectional areas of the individual compartments or feed zones so as to effect a similar proportioning by weight or by volume of the interspersed amounts of granular material being introduced solely by gravity-flow from different supply vessels and/or supply zones. Furthermore, the proportioned rate of flow of the separate granular streams as they are discharged into the individual feed compartments are completelyv self-regulating without 1. Apparatus for the continuous, self-regulating, gravityflow mixing of a pourable granular material comprising in combination:

at least one supply vessel associated with a plurality of discharge conduits for gravity-flow withdrawal of the granular material from different supply zones thereof;

an elongated vertical receiving container of rectangular cross section arranged below said supply vessel, said container having a unidimensionally narrowing discharge zone at its lower end formed by oppositely disposed walls slanting downwardly and inwardly with a narrow discharge slot at their bottom end, the angle of aperture formed by said slanting walls being smaller than 0.8 times the difference between and twice the angle of slide of the granular material, and said container having a feed grate arranged at its upper end composed of a plurality of individual compartments subdividing the rectangular cross section .of the container into a grid of feed zones in feed connection with said discharge conduits, that portion of the rectangular container between its discharge zone and said feed zones being essentially free of any obstruction to form a stabilizing zone which has a vertical height greater than the product of its width and the tan' gent of the angle of slide of said granular material; and

means to regulate the rate of flow of said granular material through said discharge slot.

2. Apparatus as claimed in claim 1 wherein the width of the stabilizing zone is less than 1500 mm.

3. Apparatus as claimed in claim 1 wherein the width of the stabilizing zone is less than 800 mm.

4. Apparatus as claimed in claim 1 wherein the ratio of the width of the discharge slot to the width of the stabilizing zone is less than 0.1.

5. Apparatus as claimed in claim 3 wherein the ratio of the width of the discharge slot to the width of the stabilizing zone is less than 0.1.

6. Apparatus as claimed in claim 1 wherein each individual discharge conduit extends vertically downwardly to open into and within a vertically positioned feed zone formed by one of said individual compartments.

7. Apparatus as claimed in claim 1 wherein said feed grate is composed of quadratic compartments of approximately equal size.

8. Apparatus as claimed in claim 6 wherein said feed grate is composed of quadratic compartments of equal size extending vertically downwardly from the top of said container, a single discharge conduit of approximately circular cross section extending vertically downwardly within each compartment such that the bottom open end of the discharge tube terminates above the lower end of the compartment. 

2. Apparatus as claimed in claim 1 wherein the width of the stabilizing zone is less than 1500 mm.
 3. Apparatus as claimed in claim 1 wherein the width of the stabilizing zone is less than 800 mm.
 4. Apparatus as claimed in claim 1 wherein the ratio of the width of the discharge slot to the width of the stabilizing zone is less than 0.1.
 5. Apparatus as claimed in claim 3 wherein the ratio of the width of the discharge slot to the width of the stabilizing zone is less than 0.1.
 6. Apparatus as claimed in claim 1 wherein each indIvidual discharge conduit extends vertically downwardly to open into and within a vertically positioned feed zone formed by one of said individual compartments.
 7. Apparatus as claimed in claim 1 wherein said feed grate is composed of quadratic compartments of approximately equal size.
 8. Apparatus as claimed in claim 6 wherein said feed grate is composed of quadratic compartments of equal size extending vertically downwardly from the top of said container, a single discharge conduit of approximately circular cross section extending vertically downwardly within each compartment such that the bottom open end of the discharge tube terminates above the lower end of the compartment. 